A local VHF radio station has its transmitting aerials in the form of
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
I would have assumed this was intended to give an omnidirectional slant-polarised radiation pattern, but I can't see how the aerials can
be connects so as to achieve both aims.
If we designate the four dipoles North, South, East and West; taking the
N-S pair, they appear to be half a wavelength apart, so if they were in
phase their vertical components in the North and South directions would cancel. If they were 180-degrees out of phase, their horizontal
components would cancel. The only way there would be both components
would be with a 90-degree (or 270-degree) phase shift. The same would
apply to the E-W pair.
If we now consider the phasing between all four aerials, to obtain an omnidirectional coverage there needs to be 90-degrees phase difference between each adjacent pair of aerials - but this is in conflict with the requirements for opposite pairs to be 90-degrees apart.
I thought I must have misunderstood how this worked, so I did a test on
the radiation. From the top of a hill on the NW fringe of the reception area, the signal is distinctly horizontally polarised. I have also
done a few random tests inside the service area, which is hilly
countryside and prone to reflections, the general impression I get is
that the horizontal component predominates and the vertical component is absent or very faint most of the time.
This is in agreement with the theory above, but I find it difficult to believe that the aerial was never intended to have a vertical componemt.
Has it been mis-wired or is it impossible to get omnidirectional slant polarisation from this type of aerial?
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
A local VHF radio station has its transmitting aerials in the form of[]
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
I would have assumed this was intended to give an omnidirectional >slant-polarised radiation pattern, but I can't see how the aerials can
be connects so as to achieve both aims.
A local VHF radio station has its transmitting aerials in the form ofThat's a Lindenblad Array
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
On 30/07/2023 10:14, Liz Tuddenham wrote:
A local VHF radio station has its transmitting aerials in the form ofThat's a Lindenblad Array
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
Further reading:-
http://on5au.be/content/storart/lin.pdf
The concept of circular polarisation isn't very helpful at VHF, as an >end-fire receiving helix of the appropriate size might generate
complaints from the neighbours.
In message <1qeozui.1pe9qh01o0q6n0N%liz@poppyrecords.invalid.invalid> at
Sun, 30 Jul 2023 17:53:57, Liz Tuddenham
<liz@poppyrecords.invalid.invalid> writes
[]
The concept of circular polarisation isn't very helpful at VHF, as an >end-fire receiving helix of the appropriate size might generate
complaints from the neighbours.
I thought circular was sometimes used as a way of ensuring there's
always a significant component of both horizontal and vertical (or
anything else the receiver uses). But I don't think it goes with omnidirectionality at the transmitter.
J. P. Gilliver <G6JPG@255soft.uk> wrote:[good explanation snipped]
In message <1qeozui.1pe9qh01o0q6n0N%liz@poppyrecords.invalid.invalid> at
Sun, 30 Jul 2023 17:53:57, Liz Tuddenham
<liz@poppyrecords.invalid.invalid> writes
[]
The concept of circular polarisation isn't very helpful at VHF, as anI thought circular was sometimes used as a way of ensuring there's
end-fire receiving helix of the appropriate size might generate
complaints from the neighbours.
always a significant component of both horizontal and vertical (or
anything else the receiver uses). But I don't think it goes with
omnidirectionality at the transmitter.
I've thought of a mental model that might explain what is supposed to
happen:
Thus the vertical and horizontal signals will be equal (circular
polariation) at the cadinal points but the horizontal signal will be
double the vertical signal at the quarter points (elliptical
polarisation).
There was the case where two Band II folded dipoles (?) were used, one It's not an unusual occurrence. Two UHF panels for Ch 5 at a site
with most of power feeding the main direction and a lower power feed
to cover another area. Unfortunately they were connected the wrong
way around. :-)
There was the case where two Band II folded dipoles (?) were used, one
with most of power feeding the main direction and a lower power feed to
cover another area. Unfortunately they were connected the wrong way
around. :-)
In message <1qeq6sp.11ex49vwp4fp2N%liz@poppyrecords.invalid.invalid> at
Mon, 31 Jul 2023 09:29:41, Liz Tuddenham
<liz@poppyrecords.invalid.invalid> writes
J. P. Gilliver <G6JPG@255soft.uk> wrote:
In message <1qeozui.1pe9qh01o0q6n0N%liz@poppyrecords.invalid.invalid> at >> Sun, 30 Jul 2023 17:53:57, Liz Tuddenham
<liz@poppyrecords.invalid.invalid> writes
[]
The concept of circular polarisation isn't very helpful at VHF, as anI thought circular was sometimes used as a way of ensuring there's
end-fire receiving helix of the appropriate size might generate
complaints from the neighbours.
always a significant component of both horizontal and vertical (or
anything else the receiver uses). But I don't think it goes with
omnidirectionality at the transmitter.
I've thought of a mental model that might explain what is supposed to >happen:[good explanation snipped]
Thus the vertical and horizontal signals will be equal (circular >polariation) at the cadinal points but the horizontal signal will be
double the vertical signal at the quarter points (elliptical
polarisation).
So for this particular arrangement, it's going to radiate circular at
the cardinal points, grading to elliptical between two of them and
vertical otherwise:
ECE
C C
ECE
A local VHF radio station has its transmitting aerials in the form of
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
I would have assumed this was intended to give an omnidirectional >slant-polarised radiation pattern, but I can't see how the aerials can
be connects so as to achieve both aims.
If we designate the four dipoles North, South, East and West; taking the
N-S pair, they appear to be half a wavelength apart, so if they were in
phase their vertical components in the North and South directions would >cancel. If they were 180-degrees out of phase, their horizontal
components would cancel. The only way there would be both components
would be with a 90-degree (or 270-degree) phase shift. The same would
apply to the E-W pair.
If we now consider the phasing between all four aerials, to obtain an >omnidirectional coverage there needs to be 90-degrees phase difference >between each adjacent pair of aerials - but this is in conflict with the >requirements for opposite pairs to be 90-degrees apart.
I thought I must have misunderstood how this worked, so I did a test on
the radiation. From the top of a hill on the NW fringe of the reception >area, the signal is distinctly horizontally polarised.
I have also
done a few random tests inside the service area, which is hilly
countryside and prone to reflections, the general impression I get is
that the horizontal component predominates and the vertical component is >absent or very faint most of the time.
This is in agreement with the theory above, but I find it difficult to >believe that the aerial was never intended to have a vertical componemt.
Has it been mis-wired or is it impossible to get omnidirectional slant >polarisation from this type of aerial?
In article <1qeodze.osdv7840rwzgN%liz@poppyrecords.invalid.invalid>, Liz Tuddenham <liz@poppyrecords.invalid.invalid> scribeth thus
A local VHF radio station has its transmitting aerials in the form of
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
I would have assumed this was intended to give an omnidirectional >slant-polarised radiation pattern, but I can't see how the aerials can
be connects so as to achieve both aims.
If we designate the four dipoles North, South, East and West; taking the >N-S pair, they appear to be half a wavelength apart, so if they were in >phase their vertical components in the North and South directions would >cancel. If they were 180-degrees out of phase, their horizontal
components would cancel. The only way there would be both components
would be with a 90-degree (or 270-degree) phase shift. The same would >apply to the E-W pair.
If we now consider the phasing between all four aerials, to obtain an >omnidirectional coverage there needs to be 90-degrees phase difference >between each adjacent pair of aerials - but this is in conflict with the >requirements for opposite pairs to be 90-degrees apart.
I thought I must have misunderstood how this worked, so I did a test on
the radiation. From the top of a hill on the NW fringe of the reception >area, the signal is distinctly horizontally polarised.
Should be equal!
I have also
done a few random tests inside the service area, which is hilly
countryside and prone to reflections, the general impression I get is
that the horizontal component predominates and the vertical component is >absent or very faint most of the time.
Shouldn't be like that normally..
This is in agreement with the theory above, but I find it difficult to >believe that the aerial was never intended to have a vertical componemt. >Has it been mis-wired or is it impossible to get omnidirectional slant >polarisation from this type of aerial?
Bit unwell to give chapter and verse right now but thats a Lindenblad invented by a bloke of the same name in the 1940's in America was used
for aircraft comms and sat comms as its gives a low angle of radiation
but mixed as such radiation, the angles and phase can vary slightly but
its essentially Ommni.
Their very good for FM broadcast used a few of them now mixed V and H
pattern and Ommni. Only downside if they don't have that much gain and
you need a top of the mast position to put them they aren't side mount animals! One here at Madingley near Cambridge sec pic down.
For a lot of stations smaller ones mainly Vertical pol is very easy to implement Horiz Ommni more difficult but in Urban areas n because of multipath and the like your RX aerial gets both V and H so if the V is
poor of polarisation skewed or shifted the whole as such is rotated so a signal is still received if you follow that!
http://tx.mb21.co.uk/gallery/gallerypage.php?txid=1138&pageid=2326
In article <Ut3m1aB09T0kFwbo@bancom.co.uk>,
tony sayer <tony@bancom.co.uk> wrote:
In article <1qeodze.osdv7840rwzgN%liz@poppyrecords.invalid.invalid>, Liz
Tuddenham <liz@poppyrecords.invalid.invalid> scribeth thus
A local VHF radio station has its transmitting aerials in the form of
four slanted dipoles:
www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
I would have assumed this was intended to give an omnidirectional
slant-polarised radiation pattern, but I can't see how the aerials can
be connects so as to achieve both aims.
If we designate the four dipoles North, South, East and West; taking the
N-S pair, they appear to be half a wavelength apart, so if they were in
phase their vertical components in the North and South directions would
cancel. If they were 180-degrees out of phase, their horizontal
components would cancel. The only way there would be both components
would be with a 90-degree (or 270-degree) phase shift. The same would
apply to the E-W pair.
If we now consider the phasing between all four aerials, to obtain an
omnidirectional coverage there needs to be 90-degrees phase difference
between each adjacent pair of aerials - but this is in conflict with the
requirements for opposite pairs to be 90-degrees apart.
I thought I must have misunderstood how this worked, so I did a test on
the radiation. From the top of a hill on the NW fringe of the reception
area, the signal is distinctly horizontally polarised.
Should be equal!
I have also
done a few random tests inside the service area, which is hilly
countryside and prone to reflections, the general impression I get is
that the horizontal component predominates and the vertical component is
absent or very faint most of the time.
Shouldn't be like that normally..
Certainly the tests I did on GLR from CP showed that the VP component came >over hills better.
This is in agreement with the theory above, but I find it difficult to
believe that the aerial was never intended to have a vertical componemt.
Has it been mis-wired or is it impossible to get omnidirectional slant
polarisation from this type of aerial?
Bit unwell to give chapter and verse right now but thats a Lindenblad
invented by a bloke of the same name in the 1940's in America was used
for aircraft comms and sat comms as its gives a low angle of radiation
but mixed as such radiation, the angles and phase can vary slightly but
its essentially Ommni.
Their very good for FM broadcast used a few of them now mixed V and H
pattern and Ommni. Only downside if they don't have that much gain and
you need a top of the mast position to put them they aren't side mount
animals! One here at Madingley near Cambridge sec pic down.
For a lot of stations smaller ones mainly Vertical pol is very easy to
implement Horiz Ommni more difficult but in Urban areas n because of
multipath and the like your RX aerial gets both V and H so if the V is
poor of polarisation skewed or shifted the whole as such is rotated so a
signal is still received if you follow that!
http://tx.mb21.co.uk/gallery/gallerypage.php?txid=1138&pageid=2326
In article <5ad05817bfcharles@candehope.me.uk>, charles <charles@candehope.me.uk> scribeth thus
In article <Ut3m1aB09T0kFwbo@bancom.co.uk>, tony sayer
<tony@bancom.co.uk> wrote:
In article <1qeodze.osdv7840rwzgN%liz@poppyrecords.invalid.invalid>,
Liz Tuddenham <liz@poppyrecords.invalid.invalid> scribeth thus
A local VHF radio station has its transmitting aerials in the form of
four slanted dipoles: www.poppyrecords.co.uk/other/SVFMtx_0432.JPG
I would have assumed this was intended to give an omnidirectional
slant-polarised radiation pattern, but I can't see how the aerials
can be connects so as to achieve both aims.
If we designate the four dipoles North, South, East and West; taking
the N-S pair, they appear to be half a wavelength apart, so if they
were in phase their vertical components in the North and South
directions would cancel. If they were 180-degrees out of phase,
their horizontal components would cancel. The only way there would
be both components would be with a 90-degree (or 270-degree) phase
shift. The same would apply to the E-W pair.
If we now consider the phasing between all four aerials, to obtain an
omnidirectional coverage there needs to be 90-degrees phase
difference between each adjacent pair of aerials - but this is in
conflict with the requirements for opposite pairs to be 90-degrees
apart.
I thought I must have misunderstood how this worked, so I did a test
on the radiation. From the top of a hill on the NW fringe of the
reception area, the signal is distinctly horizontally polarised.
Should be equal!
I have also done a few random tests inside the service area, which
is hilly countryside and prone to reflections, the general impression
I get is that the horizontal component predominates and the vertical
component is absent or very faint most of the time.
Shouldn't be like that normally..
Certainly the tests I did on GLR from CP showed that the VP component
came over hills better.
But was that a Lindenblad array Charles?.
We provide some relays off the Cambridge Madingley TX and at those relay
site locations we rotated the RX aerial and each plane was within .5 dB
of the other!...
I don't know if I ever knew about the tx antenna, Using a Yagi for
reception there was equal H & V in open sight of the tx, but VP cleared >hills better.
I don't know if I ever knew about the tx antenna, Using a Yagi for >reception there was equal H & V in open sight of the tx, but VP cleared >hills better.
Now didn't someone do some research to prove that HP went greater
distances and was that at the birth of Band Two or the advent of band 3 maybe?...
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